1. Field of the Invention
The present invention relates in general to an arrangement of an emission control system in a motor vehicle, and more particularly to an arrangement of an emission control system of a type which includes an activated charcoal canister.
2. Description of the Prior Art
In order to prevent the escape of fuel vapors from the fuel tank and the intake system of an internal combustion engine, evaporative emission control systems (EECS) have been widely employed in modern motor vehicles. In the systems, an activated charcoal canister is used to trap the vapors when the engine is shut off. Upon restarting, a flow of filtered air through the canister purges the vapors from the canister. The vapors go through one or more tubes (purge line) feeding into an induction passage downstream of a throttle valve of the intake system, and they are burnt in the engine.
However, the evaporative emission control systems hitherto proposed hitherto proposed fail to prevent the escape of fuel vapors when the fuel tank is under fuel feeding. In fact, during the feeding, fuel vapors escape from a mouth of a fuel filler tube.
In order to suppress or at least minimize this undesired matter, a measure of using an extra canister has been proposed, which is disclosed in Japanese Patent First Provisional Publication No. 60-199727.
This measure will be outlined in the following with reference to FIG. 3 of the attached drawings.
Numeral 1 denotes a fuel tank in which fuel "F" (gasoline or the like) is contained with a certain vapor space "S" remained thereabove. An evaporation tube 3 extending from an activated charcoal canister 5 is connected to the ceiling of the fuel tank 1 and exposed to the vapor space "S", so that fuel vapors produced in the fuel tank 1 flow in the tube 3 and is trapped by the canister 5. The canister 5 is mounted in an engine room of an associated motor vehicle. Upon restarting of the engine, the vapors in the canister 5 are purged by a flow of filtered air therethrough and fed to an intake system of the engine through a feeding tube 5a.
Denoted by numeral 4 is a ventilation tube which has one end projected into the fuel tank 1 and the other end connected to another or extra activated charcoal canister 6. The canister 6 is mounted in a rear portion of the vehicle where the fuel tank 1 is arranged. The canister 6 has a discharging tube 6a which is led to an open air. A switch valve 4a is connected to the ventilation tube 4, from which a tube 4b extends. A fuel filler tube 2 is connected at its lower end to a lower portion of the fuel tank 1. A fuel inlet opening or mouth 2a of the fuel filler tube 2 is equipped with a suitable seal device which is constructed to suppress or at least minimize the escape of fuel vapors when a fuel feeding is being carried out with a fuel feeding gun 7. As shown, the other end of the tube 4b extending from the switch valve 4a is connected to an inlet part of the fuel filler tube 2. Thus, fuel vapor-contained air led to the ventilation tube 4 is cleaned by the canister 6 before discharging into the open air.
However, the above-mentioned emission control system still has the following drawbacks originating from the position where the extra canister 6 is placed.
That is, usually, the mechanical strength of the rear portion of the vehicle body is considerably poor as compared with that of the engine room. Mounting the canister 6 to such a mechanically poor portion induces a considerable possibility of damaging or collapsing the canister 6 upon a vehicle collision, particularly when the vehicle is struck from behind. The collapse of the canister 6 is quite dangerous because it may bring about a fire.